I've spent alot of time in alot of different forums for alot of years and this is only the 2nd place I've came across that uses it as " She Who Must Be Obeyed".
The most common use I have seen it used for is "Son Wife Mother Brother Other" and pretty much an easier way if saying whoever is helping you do whatever. We don't need to know its your sisters first husband now married to you niece twice removed.

Maybe some people should step up and wear the pants in the family around here.